The invention relates to organophilic clay complexes capable of suspending materials and imparting thixotropic properties to aqueous coating systems such as latex paints and caulks.
Rheological agents are added to thicken aqueous systems and to produce thixotropic flow characteristics for proper brush, roller or spray applications. Prior art thickening agents for aqueous systems possessed various defects which are overcome by compositions and processes within the scope of the present invention.
These thickening agents included many organic polymers such as hydroxyethyl cellulose, carboxymethyl cellulose, quar gum or acid containing polyacrylates, partially hydrolyzed polyvinyl acetate, polyvinyl pyrolidone etc. In the last decade, numerous water soluble synthetic polymers known as associative thickeners have been introduced to coating composition for controlling application properties. These thickeners are polymers with water soluble backbone containing long chain hydrophobic pendants. U.S. Pat. Nos. 4,077,028 and 4,426,485 describe thickeners of such composition.
However, there are various problems associated with the use of these thickeners. In one form the prior art teaches a high molecular weight hydroxyethyl cellulose used as the thickening agent for latex paints. Hydroxyethyl cellulose is a solid metal material which must be dissolved before addition to the coating system which adds additional cost. Cellulose derivatives are known to have high "low shear viscosity" and low "high shear viscosity"; the fast viscosity recovery causes poor flow and leveling in paint application. In addition the elastic property of cellulose derivatives gives severe roller spatter. Moreover, cellulose derivatives are subject to microbial degradation and thus requiring the addition of preservatives. Preservatives are not only expensive, they are also a cause of enviromental concern.
A second prior process teaches the use of acid containing polyacrylates as aqueous thickener. This type of thickener is pH dependent, so before the agent will become sufficiently thickened to suspend the mixture, the pH must be carefully adjusted to the basic range.
The third prior process teaches hydrophobicly modified polyurethane or acrylic polymers used as thickening agents. Both the polyacrylates and hydrophobicly modified polymers give improved flow, leveling and roller spatter; however they have poor sag control and poor brush pickup. They are also very expensive.
Finlayson, et al, U.S. Pat. No. 4,412,018 teaches an organophilic clay gellant reacted with a quaternary ammonium, phosphonium or sulfonium compound consisting of alkyl chains and aralkyl chains or mixtures thereof; with each carbon chain consisting of 1 to 22 carbon atoms attached to the specific central element chosen for the cationic compound. However, the use of the aforementioned process is limited to non-aqueous systems, contrary to the present invention.
Mardis et al U.S. Pat. No. 4,391,637 teaches an organophilic clay reacted with a quaternary ammonium compound containing a first chain consisting of a beta, gamma, unsaturated alkyl group or a hydroxalkyl group having 2 to 6 carbon atoms; a second member containing a long chain alkyl consisting of 12 to 60 carbon atoms; and a third and fourth member, each consisting of aralkyl and alkyl or combination thereof containing 1 to 22 carbon atoms for use in non-aqueous systems.
Dohman, et. al. U.S. Pat. No. 3,298,849 describes the use of alkanolamine salt modified clay in the formulation of aqueous base paint to increase hydration rate and control rheological properties.
No prior art method or composition is known utilizing organoclay made by a polyether substituted quaternary ammonium compound as a rheological additive in aqueous paint systems.